I purchased the Canon 100-400mm, f4.5-5.6 IS lens about a year ago. At the time of purchase the lens was used on a Canon 10D with excellent results, very sharp pics. Recently, I've purchased a Canon 20D and have had problems with sharpness using this lens.Questions; "A.Is this lens not compatible with the 20D? B. Can a lens like this need calibration and some type of maintenance?" Any help would be appreciated.

I am seeing posts like this all over the popular forums and, frankly, I find it disturbing. Why are so many lenses needing to be sent back to Canon for recalibration?

Is it an issue where the lens has just adjusted itself to be out of wack or is this a compatibilty issue with the new camera (20D). If its the latter, then I have to laugh at everyone who is afraid to buy a 3rd party lens from Sigma or Tamron because of future compatibility problems like the recent "rechipping" issues.